The visual dosing aid (VDA) was developed to facilitate dosing calculations in response to children's; growth and weight during antiretroviral treatment. The theoretical accuracy of the VDA was assessed using anthropometric data from 55 children receiving care in the USA and 324 children in the Democratic Republic of the Congo. The VDA dose was similar to the WHO recommended dose. A potentially significant relative dosing difference of >or=20% occurred in <3% of children for NVP, AZT and d4T, but was observed in 20% for 3TC, overdosing being more frequent. The VDA compared well with generic pediatric fixed dose combination tablets. Results did not differ between sites. The VDA enables accurate dosing of pediatric ART in distinct populations and could facilitate roll-out of pediatric ART in resource-poor settings.